(1) Field of the Invention
The present invention relates to a plastic vessel having an oriented coating and a process for the preparation thereof. More particularly, the present invention relates to a coated oriented plastic vessel, in which such properties as the adhesion of a vinylidene chloride copolymer coating to a substrate, the whitening resistance and the gas barrier property are highly improved, and a process for the preparation thereof.
(2) Description of the Prior Art
Plastic bottles formed by melt-extruding a thermoplastic material such as a polyolefin and hollow-molding (blow-molding) the melt are used in various fields instead of glass bottles because they are lighter in the weight than glass bottles and are excellent in the impact resistance.
General-purpose plastics such as polyolefins are excellent in the moisture resistance and sanitary characteristics, but they have a relatively large oxygen permeation coefficient and permeation of oxygen through the vessel wall cannot be neglected. Therefore, these plastic materials are not suitable for the production of vessels to be used for preserving foods for a long time or cosmetic vessels for which a high perfume-retaining property is required.
As vessels in which this defect is eliminated, there have already been developed plastic bottles comprising a resin excellent in the oxygen barrier property as a vessel wall-constituting component. Among melt-extrudable thermoplastic resins available at the present, a saponified ethylene-vinyl acetate copolymer (ethylene-vinyl alcohol copolymer) is most excellent in the oxygen barrier property. However, this saponified copolymer is poor in the moisture resistance, that is, the water vapor barrier property, and in this saponified copolymer, the oxygen permeation coefficient tends to prominently increase with increase of the humidity. Therefore, when this saponified copolymer is practically used for the production of plastic bottles, the saponified copolymer is sandwiched with a moisture-resistant resin such as a polyolefin and the resulting laminate is used, which is very troublesome.
Plastic bottles formed by biaxially draw-blow-molding a parison of a polyester composed mainly of ethylene terephthalate units are now used as packaging vessels for beverage or beer. Plastic bottles of this type are light in the weight and excellent in the impact resistance, but they are defective in that the life is considerably shorter than the life of glass bottles.
It is known that a vinylidene chloride copolymer is excellent in the barrier property to various components. For example, the specification of U.S. Pat. No. 3,922,451 teaches that when a latex of a vinylidene chloride copolymer is applied to the inner surface of a metal vessel or plastic vessel and the latex is dried under certain conditions, a protective coating excellent in the continuity and adhesion to the substrate can be formed.
However, as the result of research made by us, it was found that the adhesion of a coating of a vinylidene chloride copolymer applied in the form of a latex to plastic substrates is still insufficient and involves a problem. More specifically, when a content is stored for a long time or the vessel is attacked by heat, pressure or a chemical, such a trouble as peeling of the vinylidene chloride copolymer coating from the plastic substrate or whitening of the coating per se is readily caused and the intended improvement of the gas barrier property cannot be attained.